Electrostrictive ceramic materials



United States atent ELECTROSTRICTIV E CERAMHC MATERIALS Joseph W.Crownover, Sherman Oaks, Calif assignor to Electric Machinery Mfg.Company, Minneapolis, Minn, a corporation of Minnesota ApplicationNovember 4, 1955 Serial No. 545,130

6 Claims. Cl. 106-449) No Drawing.

The earlier application discloses an invention which seeks to utilizethe electrostrictive properties of high dielectric ceramic materials andto provide ceramic materials having enhanced electrostrictivcproperties. The invention of this application provides improvedelectrostrictive ceramic materials and compositions in which the desiredcharacteristics are otherwise improved and stabilized and in which thereproducibility of the materials is improved.

In the improved compositions of this invention, the electrostrictiveproperty of the material has been enhanced and stabilized and thepiezoelectric property has been rendered insignificant or negligible.The electrostrictive composition of this invention is adapted for use invarious types of transducers, such as switches, relays, motors, loudspeakers, etc., and makes possible the practical design and applicationof many new types or" transducers wherein electrical impulses aretransduced into mechanical motion which was otherwise not possible. Theceramic materials of this invention are materials which retain only anegli iole or insignificant polariza tion charge, and the significanceof this is that if polarization of the ceramic may be retained andincreased, it may also be decreased with the result that the ceramic asan actuator or transducer is unstable and is not prac tical for use inmany types of transducers, such as relays. In the compositions of thisinvention in which the electrostrictive property is utilized, the lack.of stability resulting from reliance on polarization charge oi the ma- Iterial is eliminated.

Electrostriction in the broadest sense of dielectrics pertains to aninterrelationship between the electric field and the deformation of thedielectric in that field. Although this includes the piezoelectricphenomenon, most authorities, in order to avoid confusion, reserve theterm electrostrictive for the efiect wherein the deformation of thedielectric material subjected to an electrostatic field is proportionalto the square of the impressed electric field, thereby being independentof the applied fields polarity. The distinction is explained in thevolume by Cady Piezoelectricity (McGrav/ dill Book Co., 1946). Where thepolarization charge is not being depended on for the deforming andactuating effect, the device operates effectively in one mechanicaldirection for either polarity of applied potential.

The compositions of this invention, which are essentially bariumtitanate ceramics, provide a very large dimensional change whensubjected to electrostatic fields,

Patented May 27, 1958 and this dimensional change results from theelectrostrictive properties of the materials.

In accordance with the foregoing, it is an object of the invention toprovide improved compositions having pronounced electrostrictiveproperties and which do not retain any significant polarization charge,comprising barium titanate composition including other compositions asadditives.

Another object of the invention is to provide improved electrostrictiveceramics comprising barium titanate as a predominating constituent andincluding as an additive calcium stannate.

Another object of the invention is to provide improved electrostrictiveceramics comprising barium titanate as a predominating constituent andincluding as additives, aluminum oxide, calcium oxide, copper oxide,iron oxide, magnesium oxide, lead oxide, silicon dioxide, strontiumoxide, zirconium dioxide, titanium dioxide, and calcium stannate.

Another object of the invention is to provide improved electrostrictiveceramics comprising barium titanate as a predominating constituent andhaving as a constituent in a minor percentage calcium stannate andtitanium dioxide and having trace additives in a range of percentages ofaluminum oxide, calcium oxide, copper oxide, iron oxide, magnesiumoxide, lead oxide, silicon dioxide, strontium oxide and zirconiumdioxide.

In general, the novel compositions of the present invention comprisefired mixtures of barium titanate and calcium stannate, and in minorpercentages additives of the compositions indicated in the table whichfollows. The general classes of compositions covered by the inventionare indicated in the table. As appears in the table, the calciumstannate content of the material will be in the range of from 2% to 8%.For most of the samples the titanium dioxide additive is .9%. As to theother additives, that is, the aluminum oxide, calcium oxide, copperoxide, iron oxide, magnesium oxide, lead oxide, silicon dioxide,strontium oxide and zirconium dioxide, these additives will be in thepercentage ranges as indicated in the table, these ranges and the rangesfor barium titanate being percentages of the composition without theadded titanium dioxide and calcium stannate.

In the preparation of the compositions of the invention, the ingredientsas indicated in the table are in the form of comminuted ceramics. Theceramic bodies may be prepared in a manner conventional with bariumtitanate electrical ceramics or ceramic films, the desired amounts oftitanium dioxide and calcium stannate in comminuted form being mixed ina resin binder and the body then formed into a film and fired usingconventional techniques. Such conventional techniques are illustrated insuch patents as Lies No. 2,539,446, Howatt No. 2,486,410 and Kulcsar No.2,735,024. Or, the preparation of the compositions may be essentially inaccordance with the method of my earlier filed application, Serial No.425,664, filed April 26, 1954. in accordance with that method, thematerials in the proportions as given in the table are mixed with aliquid thermoplasticresin and a suitable plasticizer in proportions toform a thick liquid adapted to flow on to a moving fiat surface in auniform.

layer. In other words, the basic materials are formed in very thinsheets of uniform thickness by a slip casting process with the ceramicparticles dispersed uniformly through a body of polymerizedthermoplastic resin. As.

an example of the composition of the liquid mix, it may comprise thecomminuted ceramic materials, a low molecular weight liquid polyvinylchloride resin and a,

suitable plasticizer. The relative Weights of the various components, asan example, are within the proportions. 10 to 12 pounds of comminutedceramic, 1 to 3 pounds. of liquid polyvinyl chloride and 1 to 3 poundsof the.

' is-uniform within very small tolerance limits. I V .the slip isdeposited on the surface, a thin layer; of part- 'in conjunction with alonger time' duration of heat treatthe Ware without deforming orinjuring it. The ware atures for sinteringare' critical and should liewithin plasticizer, with exactpropqrtions depending upon the thicknessof the slip desired.

These ingredients are mixed to form a liquidhaving a viscosity similartothat'ofa heavy paint. :Theliquid is then deposited upon -a pro-heated.moving. surface in. such away that thethickness of the thin layer, orslip,

' Before ing agent, such as mineraloil, is sprayed thereon in order toprevent coagulation of portions of the thin layer, or

slip, after deposition thereof upon the moving snrfac'e; and also to aidin the removal of the product therefrom after subsequent heat treatment.

The moving surface, which may comprise a thin metallic member, ispreheated to a temperature somewhat in above the polymerizationtemperature of the resin used and when the thin layer of slip isdeposited on the] surface, those portionsof the layer adjacent to'theheated surface will be momentarily heated to the polymerizationtemperature of the resin, resulting in the formation 2 of an-adherentfilm of liquid on the surface. The fact that polymerization is inducedin that portion of the resin in intimate contact with the surface 'issufiici-ent to aid materially in the production of a uniformly thinlayer, or film, of slip material.

The thin slip layer is next subjected to an elevated temperature for alength of time suificient to complete the 'curing of the resin toproduce a tough, flexible sheet or ware withinv which the ceramic.particles are surrounded ment of the slip.

cated in the table by the figure appearing under the heading identifiedas strain factor. This-factor" is= rep-' resentative of theelectrostrictive response ofthe materialto appliedvoltage. In' thesecompositions, the amount of the trace additivesin each compositionwasin'ithe percentage range indicated in the table. The compositions inthe table are arranged in the. order first of increasing percentage ofcalcium'stannate and then increasing percantage of titanium dioxide. inthe strain factor, it is shown by the table that the strain factor issubstantial for all of the compositions shown within the range of 2% to8% of calcium stannate.

trio and respond to theapplicationxof voltage in thc;

same sense irrespective of its polarity," that is, they are not chargedeither before or during their use in various types of transducers. 1

With further reference to the hereinafter set forth table,

it will be noted thatwith barium titanate of'95.61%

purity, i. e. containing 4.39% by weight of trace additives: 30

and with the minimum percentages of titanium dioxide (0.9) and calciumstannate (2.0),,thepure barium titanate and trace additives willconstitute 97.1% by weight 7 of the electrostrictive material.

of purity of the barium titanate, the traceadditives will constitute4.26% by weight of the material. r

13 110 A1 CaO, OuO F6203, MgO, PbO, SiO SrO, ZlOz, T102, 0581103, Strainpercent percent percent 7 percent percent percent percent percentperpercent perpercent Factor Samplef I p r cent cent 1 0, j r

98. 91-95. 61 0. 45-0. 75 0. 020-030 002-. 006 005-0. 1 0l. 50 01-. 2430-1. 50 .3-. 90 005-. 20 9 2.0 4. 6 A T 98. 91-95. 61' 0. 45-075 0.020-0. 30 .002-. 006 .005-0.l .01. 50 0l. 24 .30-1. 50 '.3-. 00 .005. 209. 6.0 I 6. 9 B 7 98. 91-951 01 0. 45-0. 75 0. 020-0. 30 002 006 005-0.1 01-. 50 01-. 24 30-1150 3-. 90 005-. 20 9 6. 5. 5 C 98. 91-95. 610.45-0.75 0. 020-0. 30 .002-. 006 .005-01 .O1.50 0l. 24 .30-1. 50: .3-.90 .005-. .9 7.0 4.8 .D" 98. 91-95. 61 0.45-0.75 0. 020-0. (102-. 000.005-0. 1- 01. 50 01. 24 30-1. 50 .3. 00 005-. 20 .9 7. 5 '6. 2 J. E 798. 91-05. 61 0. -0. 75 0. 020-0. 30 002-. 000 005-0. 1- 01-. 01. 2430-1. 50' 3-. 90 005-. 20 S) 8. 0 4. 8 F. 98. 91-95. 61 '0. 45-0. 750020-0. 30 002-. 006 005-0. 1 V 101-. 50 01-. 24 .30-1. 50 13 90 005-.20 1. 25 7. 5 7; 4 "G 98. 91-95. 61 0. 45-0. 75 0. 020-0. 30 002-. 006005-0. 1 0l. 50 01. 24 30-1. 50' 3- 90 005-. 20 l. 5 7. 5 1 '5. 8 TH;

Removal of the ware from the metallic surface is I claim:

effected by means of a-knife or blade setat a slight angleto the surfaceand in contact therewith to separate is then cut to size and baked atthe sintering temper ature of the ceramic to bring about burning out'ofthe polymerized resin and .to induce combination and unit-. ing togetherof the ceramic particles. QT he oven temperthe range 2430? to 2460i Forexample, slntering of a'sample of Ware at 2440 for one hour gives veryfavorable results. 1 Y r The ceramic-materials having compositions as inthe foregoing wereformed into thin sheets and for p urpose v ofexamining their electrostrictive properties, the sheets.

'were' cut into strips of suitable .widthand length.

Electrodes were applied to oppositefacesof the strips and a preferredway of .doing this is by painting the opposite faces with silver painterother electrically conductive of arr-actuator, for example, it maybemounted'asa' cantilever member or it maybe mounted at bothends'.

'Theyapplic'ation of voltage between theelc'ctrodes. will 7 'resultirran expansionofthe material in the direction-'70 between theelectrodesand-aconstriction or contraction.

- in the other dimensions. JLThe effect is quadratic',,,asshasi i beenexplained inthefparent application referredto above That is,thejdeformationofthefmaterial is; in. the same.

' and 09% to 1.5% by weight of titanium dioxide.

material; Such a stripmay be'mounted in the-manner 1. A fired ceramicelectrostrictive'material-composed of barium titanate having not morethan 4.39% -by Weight of trace additives and containing-2% to 8% 7weight of calcium. stannate and 0.9% to 1.5% by weight 'of titaniumdioxide. i 1 1 v 2. A fired ceramic electrostrictive material composed.of barium titanate having not more than 4.39%"hy weight of traceadditives including traces of metal oxides and containing 2% to 8% byweight of calcium stannate 3. Aflfired ceramic electrostrictive materialcomposed titanium dioxidep e h V 4. A barium titanate electrostrictivematerial composed of a composition expressed as BaO, TiO S110 and'CaOsuch that the C210 and SnO are combined to' give a calciumstannateconteht of 2% to 8% by iweightl f and there is sufiicient TiO.to combine with all, of' the i weight. 7,

5. A barium BaO to leave an excess of T10 0f 0.9% to 1.5 by

The mag-, nitude of the response, that :is-, the deformation, is indi-While there is variation 7 Thus, with this degree 7 7 p H titanateelectrostrictive material comsense irrespective of'the polarity oftheiappli'ed'voltage. posed of a composition expressed, as B210, TiOSilos 5 and C210 and including traces of metal oxides of not more than4.26% by weight, the CaO and SnO being combined to give a calciumstannate content of 2% 'to 8% and there being suflicient TiO to combinewith all of the BaO to leave an excess of TiO of 0.9% to 1.5% by weight.

61 A barium titanate electrostrictive material composed of a compositionexpressed as BaO, Ti0 SnO and CaO and including traces of A1 0 CuO, Fe OMgO, PbO, SiO S10 and Zr0 totalling not more than 4.26% by Weight, theCaO and SnO being combined to give a calcium stannate content of 2% to8%; and there 6 being sufficient Ti0 to combine with all of the BaO toleave an excess of TiO;, of 0.9% to 1.5% by weight.

References Cited in the file of this patent UNITED STATES PATENTS2,402,515 Wainer June 18, 1946 2,452,532 Wainer Oct. 26, 1948 2,705,204Shen et a1. Mar. 29, 1955 FOREIGN PATENTS 698,946 Great Britain Oct. 28,1953

6. A BARIUM TITANATE ELECTROSTRICTIVE MATERIAL COMPOSED OF A COMPOSITIONEXPRESSED AS BAO, TIO2, SNO2 AND CAO AND INCLUDING TRACES OF AL2O3, CUO,FE2O3, MGO, PBO, SIO2, SRO AND ZRO2 TOTALLING NOT MORE THAN 4.26% BYWEIGHT, THE CAO AND SNO2 BEING COMBINED TO GIVE A CALCIUM STANNATECONTENT OF 2% TO 8%, AND THERE BEING SUFFICIENT TIO2 TO COMBINE WITH ALLOF THE BAO TO LEAVE AN EXCESS OF TIO2 OF 0.9% TO 1.5% BY WEIGHT.